a) Field of the Invention
The present invention relates to low dielectric constant film materials, and to low dielectric constant films and semiconductor devices using such materials.
b) Description of the Related Art
Higher integration and higher speed of semiconductor integrated circuits are desired. A signal transmission speed in a semiconductor integrated circuit is restricted by wiring resistance and parasitic capacitance between wiring lines. Wiring resistance and parasitic capacitance are increasing as the wiring width and pitch are becoming narrow because of higher integration of semiconductor integrated circuits. Although parasitic capacitance can be reduced by thinning wiring lines, wiring resistance increases and the reduced capacitance does not contribute to improving the signal transmission speed. In order to increase the signal transmission speed, it is effective to make an inter-level insulating film have a low dielectric constant.
Conventionally, an inter-level insulating film is made of non-organic material such as silicon dioxide (SiO2), silicon nitride (SiN), silicon oxyfluoride (SiOF) and phosphosilicate glass (PSG), or organic polymer such as polyimide. A relative dielectric constant of a silicon dioxide film formed by chemical vapor deposition (CVD) is about 4. A relative dielectric constant of a SiOF film is about 3.3 to 3.5 which is lower than that of silicon dioxide. However, since SiOF has a high moisture absorption rate, a SiOF film is likely to absorb moisture and raise its relative dielectric constant.
As low dielectric constant materials, attention has been paid to siloxane resin having Sixe2x80x94H bonds, porous siloxane resin or the like.
As siloxane resin is washed with alkaline solution, SiOH having a high moisture absorption rate is produced because of hydrolysis. Therefore, siloxane resin washed with alkaline solution raises its relative dielectric constant. Apart from this, an organic polymer film has as low a glass transition temperature as about 200 to 350xc2x0 C. and a high thermal expansion coefficient. Damages to wiring layers are therefore large.
It is an object of the present invention to provide materials of low dielectric constant films suitable for inter-level insulating materials.
It is another object of the invention to provide low dielectric constant films suitable for inter-level insulating films.
It is still another object of the invention to provide semiconductor devices having low dielectric constant films and high reliability.
According to one aspect of the present invention, there is provided a low dielectric constant film forming material containing siloxane resin and polycarbosilane dissolved together.
According another aspect of the invention, there is provided a low dielectric constant film made of siloxane resin and polycarbosilane bonded to the siloxane resin.
According to another aspect of the invention, there is provided a semiconductor device comprising a semiconductor substrate and a dielectric film disposed on the principal surface of the semiconductor substrate and made of low dielectric constant material containing siloxane resin and polycarbosilane bonded to the siloxane resin.
By adding polycarbosilane to siloxane resin, resistance against alkaline of a siloxane resin film can be improved.
According to another aspect of the present invention, there is provided a semiconductor device comprising: a semiconductor substrate; a first film formed on a surface of the semiconductor substrate and made of a first silica-containing porous material; and a second film directly formed on the first film and made of a second silica-containing porous material, the second silica-containing porous material having an etching rate different from an etching rate of the first silica-containing porous material under a same etching condition.
According to another aspect of the invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: forming a first film made of a first silica-containing porous material on a surface of a semiconductor substrate; forming a second film of a second silica-containing porous material directly on a surface of the first film, an etching rate of the second silica-containing porous material being faster than an etching rate of the first silica-containing porous material; forming a trench having a depth greater than a thickness of the second film and a via hole through the first film, the via hole being partially overlapped by the trench; and burying a conductive material in the via hole and trench.
By using silica-containing porous material as the material of the first and second films, a dielectric constant can be lowered. Since the etching rates of the first and second films are different, it is easy to selectively etch only one of the films.
As above, by adding polycarbosilane to siloxane resin, resistance against alkaline of a low dielectric constant film can be improved. Therefore, a dielectric constant of a low dielectric constant film can be maintained low even after a process using alkaline solution.
By stacking a film made of silica-containing porous material having a faster etching rate upon a film made of silica-containing porous material having a slower etching rate, etching the upper layer can be stopped with relatively good controllability when the lower film is exposed.